yes, all sorts of data comparison of before and after the event being measured on Earth! soooo intriguing!
I read about a longterm Pulsar project in which the goal is to detect GW passing by their system by constantly measuring it's pulse and looking for deviations (Pulsar J1909-3744). Their object of interest is 195 light years away somewhere in Taurus.
So, without knowing exactly where the two BH merged, it's still possible that the GW already have passed by the Pulsar, too, and the deviation stayed undetected. Or maybe it will take another 100 light years for the GW to reach J1909. I don't know.
How exciting is the stuff the Pulsar project members can learn about their assumptions and methods, now, that they know they didn't see what they were looking for, even though it was indeed there: marvellous!
(The article I had read bout it was pre-discovery publication so it didn't state anything about them crawling back into the data or anything, yet.)
Or the Ligo teams themselves:
they can try and understand why their two "rulers" measured different amplitudes in the build-up - and only during the merger-moment became quite congruent.
>>image
It could be a tool's problem of one or the other Ligo - or both.
Or it might be a predictable GW behaviour, previously unthought of. Especially in the light of congruent "chirp" in the merging moment. Assuming if there was problem with the tool, the merging moment would not show up as congruent as it was, either.